Where a stent is indwelled at a stenosed lesion area of a living body lumen such as a blood vessel, biliary duct, esophagus, trachea, urethra and other organs to secure the lumen, catheters attached with a balloon (i.e., balloon catheters) can be used for treating ischemic heart disease or for urethral catheterization for a patient who has difficulty urinating.
It can be desirable for the balloon for catheter to have various characteristics including (1) trackability (ability to track meandering blood vessels), (2) ability to pass through a stenosed lesion such as in blood vessels), (3) ability to dilate a stenosed lesion such as in calcified blood vessels, (4) a compliance characteristic (an appropriate degree of non-distensibility sufficient for not causing a great change in balloon diameter depending on a small pressure change) and strength or pressure resistance sufficient to withstand an inner pressure or impact upon balloon inflation.
It can be desirable for catheter balloons to have such safety that the possibility of causing damages against a blood tumor or blood vessel can be minimized as small as possible. Accordingly, a characteristic of not causing a great change in balloon diameter depending on a small change in pressure, i.e., a compliance characteristic, can be one of the most important characteristics. A technique in which attention has been paid to this compliance characteristic is described, for example in U.S. Pat. No. 6,488,688 B2. In U.S. Pat. No. 6,488,688 B2, there is proposed a semi-flexible balloon formed of a polyurethane block copolymer and showing a rate of change of 0.025 to 0.045 mm/atm within an inflation pressure range of from 6 atm to 19 atm, and an axially inflexible balloon formed of a polyurethane block copolymer and showing a rate of change of 0.01 to 0.25 mm/atm within an inflation pressure range of 6 atm to 14 atm.
Other technology is proposed in U.S. Pat. No. 5,769,817. In U.S. Pat. No. 5,769,817, a balloon, which is formed of a double-wall tubular member constituted of a polyamide for the outermost wall and polyethylene terephthalate for the innermost wall, shows a compliance coefficient of not larger than 13% over a pressure range of 8 to 18 atm.
It is stated in U.S. Pat. No. 5,769,817 that this balloon is able to suppress the wear ascribed to the frictional phenomenon between the balloon and a stent when in use for stent delivery and is excellent in non-distensibility contributing to suppress excess expansion of a stent against blood vessel and also in burst strength.